Not a lasting last for the Neandertals
The latest in a long line of "last known Neandertal" sites is now Gorham's Cave, Gibraltar. Of course, if this were actually a continuing string of "latest" sites, you would expect we would eventually either reach the present day, or some mathematical limit. There seems to be little danger of that happening for a while, though, since the previous "last known Neandertal" sites keep turning out to be older than their "first known" radiocarbon dates!
The current paper by Clive Finlayson and colleagues has a good short review of this issue:
The sequence of radiocarbon dates presented, including 14 dates at or statistically younger than 30 kyr bp, are the only currently reliable ones that establish the persistence of Neanderthals and associated Mousterian technology after 30 kyr bp. Earlier claims are now dismissed or are uncertain for a variety of reasons and in particular after the revision of dates on bone with the use of ultrafiltration treatment, a treatment only meaningful for dates on bone. Hyaena Den (UK) is now considered older than 30 kyr bp; the Vindija (Croatia) Neanderthals have been re-dated to between 32 and 33 kyr bp or older; Zafarraya (Spain) is now discarded for several reasons; the Mezmaiskaya, Russia, Neanderthal is now dated to at least 36 kyr bp. The single AMS date on Cervus bone for Caldeirão (Portugal) will require revision and is likely, given the result for Hyaena Den of similar age, to be older than 30 kyr bp. Finally, the single 14C date, from Patella shells, from Figueira Brava, Portugal, is not statistically younger than 30 kyr bp (Finlayson et al. 2006, references omitted).
So are the current radiocarbon dates for Gorham's Cave any better? Or, to put it another way, why exactly should we believe any new claims about recent dates, given the long list of dates that we are now supposed to forget about?
Now, I'm not an archaeologist, nor am I a geochronologist. So maybe I'm missing something. But look at this figure from the paper (Figure 1c):
Section from Gorham's Cave, showing points of radiocarbon sampling, Figure 1c from Finlayson et al. (2006).
Notice sampling points 16, 17, and 20. Those are the key samples for the paper's conclusion:
Thus, three samples (16, 17 and 20; Fig. 1) came from in situ Mousterian superimposed hearths. These three dates provide a stratigraphic sequence from 24,010 +- 320 to 30,560 +- 720 yr bp. Taken together, all the dates show that Neanderthals occupied the site until 28 kyr bp and possibly as recently as 24 kyr bp. The evidence in support of the 24 kyr bp date is more limited than for 28 kyr bp, which is taken as the latest well-supported occupation date (Finlayson et al. 2006).
OK, so we have three samples from the same place in the cave, over a short vertical distance, that appear to represent successive occupations over a few-thousand-year interval. The authors interpret conservatively that maybe the 24,000-year date is too young to be Neandertal -- although they don't describe just what makes the evidence "more limited," considering each date is supported by a single radiocarbon sample.
But look at sample number 11 in the figure. It appears to have been taken from directly above the putative hearths. So why does it have a date of 27,020 +/- 480 years?
I think we begin to detect why there is "more limited" evidence for the 24,000-year date. It is directly controverted by the sequence.
Moreover, we have to doubt the 26,000-year date, considering the evident contamination and/or turbation of the sample directly above it.
Am I saying the Neandertals weren't in this cave after 30,000 years ago? Well, if you look at the samples in the figure, and their locations, almost all the samples taken from the brown zone (layer IV) have dates between 28,000 and 32,000 years BP. But there are several with dates between 26,000 and 23,000 years, and these are mixed in amongst or below earlier dates in the 28,000-30,000 year BP range.
Please check out the dates yourself: Sample 23 (23,360 BP) is directly below sample 22 (29,720 BP). Sample 9 (26,070 BP) is directly adjacent to sample 10 (28,360 BP). Sample 15 (23,780 BP) appears to be stratigraphically below sample 14 (30,310 BP), although these are more spatially distant. Sample 28 (28,170 BP) is immediately below sample 27 (31,850 BP). Sample 29 (29,210 BP) is directly below sample 25 (31,780 BP). In all cases these discrepancies are outside the reported confidence limits.
There seems to be clear evidence of widespread movement of material or contamination in this sequence.
So, does the sheer weight of dates between 32,000 BP and 28,000 BP lead to the conclusion that the cave was occupied by Neandertals during that time range? Maybe so, but I think the paper raises a lot more questions than it answers. I have to think that we'll be hearing about how this date is equivocal or problematic, instead of it being the "latest Neandertal."
References:
Brill D. 2006. Neanderthal's last stand. Nature News 13 Sept. 2006. DOI link
Finlayson C, and 25 others. 2006. Late survival of Neanderthals at the southernmost extreme of Europe. Nature, advanced online publication doi : 10.1038/nature05195
Pendergast DM. 2000. The problems raised by small charcoal samples for radiocarbon analysis. J Field Archaeol 27:237-239.
Grotte des Fées de Châtelperron
Gravina et al. (2005) report on the radiocarbon stratigraphy of this cave, which is the original type site of the Chatelperronian industry. I think the paper is a very fine example of most archaeological papers I have read. The thing is, like many other papers, I'm not sure it provides enough information for me to understand the conclusion.
The most relevant finding is this:
Hitherto, direct archaeological evidence for [the temporal overlap of Chatelperronian and Aurignacian industries] has proved controversial, with the suggestion that supposedly direct 'interstratifications' of Chatelperronian and Aurignacian levels at three separate sites in western France and northern Spain (Roc de Combe and Le Piage in southwest France, and El Pendo in northwest Spain) might in fact reflect serious confusions or misinterpretations of the stratigraphy at these sites. The results reported here seem to provide clear evidence for a direct interstratification of distinctively Chatelperronian and Aurignacian occupations at the type-site of Châtelperron itself, closely dated by a sequence of 13 high-resolution radiocarbon accelerator mass spectrometry (AMS) measurements by the Oxford Radiocarbon Laboratory (Gravina et al. 2005:1).
The stratigraphy by itself would seem to be adequate for the conclusion: there are 10 typologically Aurignacian artifacts with provenience from the Chatelperronian levels, two perforated animal teeth consistent with Aurignacian typology, and nineteenth-century excavations recovered three unprovenienced Aurignacian blades and one split-based bone or antler point. The interpretation of "interleaving" comes from the observation that the majority of the provenienced Aurignacian artifacts came from one level (B4) of the Chatelperronian, both above and below other Chatelperronian levels (B1-B5). If these typologically Aurignacian artifacts were made by modern humans, then they demonstrate the temporal overlap of Neandertals and modern humans at the site.
Compared to this--a careful historical review--the dates are a bit of an anticlimax: 40,000 radiocarbon years for the bottom of the sequence, 34,500 to 36,000 for the top, and between 39,000 and 36,000 for level B4 with many of the Aurignacian-type artifacts.
The authors attempt a comparison between these radiocarbon dates and the Cariaco Basin deep sea core, which leads them to an interesting argument:
What is clear from the Cariaco basin data is that the overall time range of the human occupation is likely to be much shorter than the range of the radiocarbon dates, with the occupation of B5 centred on 42,000-43,000 yr BP, B4 on ~41,000-42,000 yr BP and that of B1-B3 on ~40,000-41,000 yr BP (ages estimated from the GISP2 ice core). Interestingly, the occupation in phases B5 and B1-B3 seems to be correlated with brief warmer spells visible in the delta 18O record. The two samples from B4 are somewhat different in age and correlate with the end of one warmer period and the start of the next, separated by an intervening colder phase. This coincides with the brief episode of Aurignacian occupation in level B4. A displacement of Aurignacian populations from central Europe to France in response to sharply colder conditions at this time (especially perhaps the onset of severe winters) would hardly be surprising in ecological and demographic terms, as winter temperatures in the more oceanic areas of western Europe are likely to have been significantly milder than those further to the east... (ibid., 5).
Interesting to me is the possibility that all this stuff actually unfolded over around 2000-3000 years of real (non-radiocarbon) time. This seems more intuitive than the persistence of distinct, static cultures across 6000 years or more, while intermittently in contact with different groups.
Reading between the lines of my description, you may sense a bit of hesitancy toward the conclusions. I'm not an archaeologist, and many of the concerns of trained archaeologists are lost on me. I wouldn't know an Aurignacian blade from a Chatelperron backed point.
But perhaps unlike many non-archaeologists, I have looked to see if I can tell the difference. I happen to have the edited volume Context of a Late Neandertal: Implications of Multidisciplinary Research for the Transition to Upper Paleolithic Adaptations at Saint-Césaire, Charente-Maritime, France on my shelf. Here are five of the Aurignacian blades from Chatelperron (Gravina et al. 2005:3):
Aurignacian edge-retouched blades from Chatelperron
Here are some of the Chatelperron backed points from Saint-Césaire, approximately to the same scale (Leveque 2003):
Chatelperron backed points from Saint-Césaire (Leveque 1993)
There is of course an obvious difference: the Aurignacian blades are retouched on both sides; the Chatelperron points are "backed", or retouched only on one side. But despite their names, the "points" are not necessarily pointier; the tools would appear to be close functional analogues.
Now here's my question: if you have a sample of 65 Chatelperron points from a site (unlike the upper Chatelperronian level of Saint-Césaire where there are only 8), how likely is it that you might find a few that look like Aurignacian blades?
The answer to that might be "very unlikely". Indeed, the fact that some of the Chatelperron "Aurignacian" artifacts are made on materials brought from far away might give an additional reason to think that they stand apart from the average Chatelperron point. And the split-based point is a likely marker of at least strong Aurignacian influence (although it is unprovenienced).
But I would be more convinced by a statistical answer to that question than a typological one. Out of those 65 backed points, how many of them have some retouch on the backed side? Any extensive? There are 750 artifacts in the Chatelperronian levels. Where did they come from? How many of them come from level H4? From the description here, it appears that the Aurignacian-type artifacts come directly from Chatelperronian layers -- that is to say, they are not "interleaved", they found with Chatelperronian-type artifacts. Is that accurate? If not, why not?
These are questions that I could ultimately answer myself through the magic of interlibrary loan, but that would take weeks. They ought to be in this paper. There is no possibility of understanding the importance of 10 atypical artifacts without some assessment of the range of variation of the "typical" ones. All this paper gives is an assertion that they are in fact Aurignacian. That they may be, but how do we know it?
Other related questions I wouldn't expect the paper to answer, but I would expect somebody else to look at soon. Are there artifacts at other Chatelperronian sites that fit these criteria? What would a finite mixture of two industries look like -- especially in the case where there is a lot of one industry and only a few artifacts of another? After all, the Aurignacian and Chatelperronian differ in a few fossiles directeurs, but for the most part they share a lot of tool types at different frequencies. Would that mix of frequencies be statistically identifiable, or would it be indistinguishable from different facies of the same industry?
Probably I'm thinking too much like a biologist. And to be honest, finite mixture analysis may be a bit much to expect from anybody.
So, the paper may be entirely correct for all I know. I'm just asking naive questions, beyond my expertise. But when two pictures look like the ones above, and they are supposed to be typologically identifiable products of "modern humans" on the one hand, and "Neandertals" on the other -- well, it seems to me there needs to be a bit more than an edge of retouch behind that conclusion.
Neandertal teeth: fast or slow?
National Geographic online is running a news story describing a new study of Neandertal dental development. The study is by Debbie Guatelli-Steinberg and collaborators and is supposed to be in PNAS early edition, but it isn't yet. When it gets there I'll post again. In the meantime:
The question of whether Neandertals, who died out some 35,000 years ago, shared the prolonged childhoods found in modern humans is a controversial one.
Other researchers who studied Neandertal tooth remains reported in 2004 that Neandertals became sexually mature adults by as young as 15 years of age (see "Neandertals Were Fully Developed by Age 15, Experts Say"). The 2004 study found Neandertal wisdom teeth grew 15 percent faster than those of modern humans.
Guatelli-Steinberg, though, says the earlier study did not take into account how variable modern populations are in their dental growth -- a criticism that was also raised at the time of the 2004 study's publication.
"We examined a much broader range of modern humans, from three different regions of the world," the anthropologist added. "When we did this we found that Neandertal [front teeth] formation spans are comparable to those of modern humans."
Personally, I think we have a long way to go in understanding the variation in growth rates in living people, before we can infer that Neandertals are very different from us in the sequence and timing of growth. That seems like it's going to be the conclusion of this work, so that sounds about right to me. This doesn't tell the whole story of Neandertal development, but it does help to establish a timeline. And teeth have a much bigger sample than the kinds of artificial growth-series of crania (from different times and places) that we are starting to see.
The mobile Neandertal
Beauval et al. (2005) report on the anatomy, mtDNA genetics, and archaeological associations of a femur shaft fragment from Les Rochers-de-Villeneuve, France.
Two aspects of the specimen have attracted interest. The first is the connection with the hyenas. The National Geographic news report focuses on this aspect:
"The Neandertals and large carnivores occupied the cave in rapid succession," said Erik Trinkaus, a paleoanthropologist at Washington University in St. Louis, Missouri. "We have the bones of herbivores like bison and deer being chewed or processed by both Neandertals and hyenas, and they're both only going to do that if the meat is reasonably fresh, and if there's still something on there to get off."
"We have this idea that once humans became reasonably successful as hunters that they walked with impunity on the landscape, and that's just not so," Trinkaus said. "I'm not saying they were having fights at the mouths of caves with the hyenas, but I'm sure there were plenty of times when the hyenas came and, not being stupid, the Neandertals said 'see ya later, guys.'"
About this, there is little to be said. Pleistocene humans generally were in strong competition with carnivores. For the Neandertals this competition may have been more important than elsewhere, because we infer that their diets were strongly dominated by meat. On the other hand, finding human cutmarks and carnivore tooth marks on the same bones does not indicate that humans were frequently (or ever) on the losing end of their encounters with carnivores. Lions and hyenas both exploit the same carcasses today, and although hyenas can be formidable opponents for lions, the lions are generally successful both in defending carcasses for as long as they want them, and in stealing carcasses from hyenas. We don't know that Neandertals had this kind of success, less, or more. Of course, the fact that the hyenas ate part of this individual (toothmarks on the femur itself) goes farther than most of the evidence toward the idea that humans were more than rarely on the losing end.
The other point of interest is the inference of increasing mobility based upon the anatomy of the femur shaft. The following is from the Washington University press release:
"In Europe, with the transition from Neandertals to modern humans, anthropologists have long argued that major behavioral changes and major improvements in adaptation began to take shape with modern humans," said Erik Trinkaus, Ph.D., Mary Tileston Hemenway Professor of Anthropology at Washington University and co-author of the paper.
"One of the changes that has been documented with the transition from Neandertals to modern humans was that people became more mobile and their territories became much larger. They became less locally focused and more regionally focused," Trinkaus said.
It's been assumed that this happened in the Upper Paleolithic which is associated with some very late Neandertals and early modern humans. However, this is a femur bone from a Middle Paleolithic Neandertal. It shows in the shape of the femur that a shift to greater mobility had already begun prior to the transition to the Upper Paleolithic, prior to any appearance of modern humans in Europe.
The pattern observed in Les Rochers-de-Villeneuve is not unique. Trinkaus and colleagues (1998) presented the cross-sectional geometry and biomechanical analysis of the femur of the Saint-Césaire skeleton. This specimen is a late Neandertal dating to around 36,000 years ago. The Saint-Césaire right femur is similar to other Neandertals in the cross-sectional geometry of its subtrochanteric region, but is different from Neandertals in its midshaft -- the same region of the bone that Les Rochers-de-Villeneuve preserves. From Trinkaus et al. (1998:5838-5839):
[T]he degree of structural anteroposterior reinforcement of the femoral midshaft of at least recent humans parallels degrees of mobility, such that, on average, males exhibit greater midshaft anteroposterior reinforcement than females, including among Pleistocene Homo, and pre-industrial populations inhabiting more accentuated terrains exhibit an emphasis on anteroposterior femoral strength. The greater femoral midshaft anteroposterior strength in the early modern human sample therefore suggests a higher average level of habitual mobility (contrasts in terrain per se are not relevant because the two reference groups occupied most of the same regions, and, if there are any differences in habitual terrain, it is more likely that the Neandertal sample experienced a steeper topography because many of the early modern human remains derive from the more open central European plains). With respect to this, Saint-Césaire 1 falls clearly with the early modern humans and separate from the Neandertals.
That paper concludes with the hypothesis that Saint-Césaire 1 represents a late Neandertal population in which the hyperarctic body proportions are maintained but mobility patterns have begun to change. Both bones are fragmentary, so the estimation of limb length (and thereby of leg length and proportions) is imprecise. But assuming that both bones represent individuals with short, cold-adapted legs, they would appear together to be significantly different from other Neandertals in their cross-sectional geometry at midshaft. According to Trinkaus et al. (1998), the Feldhofer 1 specimen is similar to these in approaching the midshaft cross-sectional geometry of Upper Paleolithic modern humans, although not to the extent of the Saint-Césaire femur. Feldhofer is also a relatively late Neandertal, now thought to date between 40,000 and 45,000 years. So there is a suggestion that later Neandertals differ from earlier ones in their femur diaphyseal anatomy, and that this difference may reflect activity to some extent.
On the other hand, the later Neandertals would also include Spy, which do not have greater anteroposterior bending strength. And it is unclear whether the variation in the late Neandertal sample taken as a group is significantly different from earlier Neandertals. What we see in these latest specimens is the hint of a change, but not strong evidence of one. This problem is ultimately one of sample size, and it would be interesting to consider the kind of variation within samples of recent humans as well as between groups with different activity patterns to see how much variation is consistent with a single activity pattern. More on this below.
What is mobility?
The mobility pattern is a way to broadly talk about the home range size, daily movement distances, annual range and long-distance movements, speed, and locomotor power. The femur reflects the influence of all of these, through their biomechanical requirements, such as the lever arms of muscles, the muscle force as a correlate of muscle size, and the joint reaction forces and biomechanical loads related to moving the mass of the body. Thus, the femur anatomy is a compromise among the many requirements placed on it.
Inferring all of these things from the geometric distribution of cortical bone in the femur diaphysis is -- at least on the face of the problem -- statistically impossible. There is really only a single variable: femur shaft breadth/depth ratio. Cortical bone area arguably is a second variable but in the absence of information about body size its utility is questionable. The variables are influenced by many parameters, including all those listed above and perhaps several more. A single variable can explain at most a single independent parameter. Thus, we have a problem: there are simply too many possible combinations of parameters that could influence shaft anatomy.
Research into mobility patterns deals with this problem by attempting to reduce the number of parameters. The most promising way to accomplish this is to show that the parameters are not independent -- that changing one of them tends to change all the others as well. Given the small number of recent foraging groups whose skeletal remains are available for study, this research effectively condenses to a small number of contrasts between "mobile" and "less mobile" or "sedentary" groups. For example, Holt (2003:204, citations elided) describes the relationship between cross-sectional geometry, muscle activity, and forager mobility:
Femoral and tibial diaphyseal morphology reflects variability in levels of locomotion. Studies of human gait show that anterior-posterior (a-p) bending moments resulting from the combined effects of hamstring and quadriceps muscle groups are highest in the knee region (midshaft femur to midshaft tibia), reflecting activities such as running and climbing. The transition from highly mobile hunter-gatherer subsistence to a more sedentary one produces important changes in lower limb bones, namely inward contraction of cortex, reduced a-p bending rigidity of the midshaft femur and tibia, resulting in reduced directionality of greatest bending strength, and increased circularity of midshaft femoral and tibial cross sections. This was elegantly demonstrated in a recent comparison of limb bone strength between Holocene southern African and Andaman Islands foragers (Stock and Pfeiffer, 2001). The highly mobile prehistoric South African foragers had significantly stronger and less circular lower limb bone shafts, while the protohistoric Andaman Islanders, who rely primarily on exploitation of marine resources by boat, exhibited more robust clavicles and humeri, in keeping with expectations from their low level of terrestrial mobility.
Thus, "mobility" is a conceptual category that includes essentially every activity that might make people walk farther, move faster, exercise more, and stay in one place less. In certain comparisons between "mobile" groups and "less mobile" groups, the more mobile groups have a cross-sectional anatomy with a greater anteroposterior diameter. In modern humans those people also tend to have a pronounced pilaster on their posterior femora, and have greater cortical bone area. As long as these components of the overall activity pattern can be grouped together into a contrast between two populations, the argument that bone anatomy responds to something called "mobility" can be supported.
There is a more extensive literature on this issue that can be reviewed from the references in these papers; I am skeptical of the relationship but please read further into these references if you are interested in the way mobility is assessed and compared between populations.
A problem with this approach is that some relatively uncorrelated parameters still remain. The most important are body mass and stature. Since recent hunter-gatherers vary substantially in both these values, studies of mobility and its effects on bone anatomy have attempted to "control for" them. But what such a control might mean when extrapolated to an extinct population with very different mass and stature than most living foragers is basically not known. It is through these values that the degree of cold adaptation becomes important. A short limb and a broad trunk may be expected to exert a greater mediolateral force on the limb bones, as the body requires more powerful muscular support during one-legged stance. Weaver (2003) asserts that much of the femur anatomy of the Neandertals is a consequence of their relatively short legs and broad pelvis. At the least, cold adaptation is a potent confounding factor that complicates the interpretation of mobility patterns from bone cross-sectional anatomy; at the worst it makes such inference impossible. The problem is also addressed by Pearson (2000) who attempts to relate robusticity to activity patterns and climate, finding that climate explains much in the robusticity patterns (rough measures of bone strength) of living human populations.
In this vein, Lieberman's (2000:595) comment is pertinent:
Since some recent humans (e.g., Australians) have levels of residual robusticity as high as those of Neanderthals, simplistic models of behavioral change which predict that technological advances from the Middle to the Upper Paleolithic led to reductions in stress levels over time are untenable. Life was apparently pretty tough for everyone in the Paleolithic but possibly in substantially different ways.
Until this kind of concern can be answered, it is not clear that any test of activity patterns in Pleistocene fossil samples will be possible. Unlike Lieberman, I don't think these answers will come from controlled laboratory experiments on living human or animal subjects. The kinds of activities that contribute to the anatomy of a hunter-gatherer femur over a lifetime are a very complex system. Reducing activity to different components and testing separate effects may have much to offer in terms of showing the relative importance of different activities within a population. But for Neandertals, the problem is inferring an unknown pattern from a single variable; and from that perspective, a fuller conception of activity patterns in living populations only further problematizes the issue. In other words, the more we learn, the less we know. For the scientist, this is how it should be, but it does not bode well for our ability to interpret changes in later Neandertals.
The multiple explanations of Neandertal mobility
But suppose we dismiss my skepticism about whether we can infer anything about activity patterns from femur cross-sectional diameter. In any event, the anatomy of the later Neandertals appears to make an interesting contrast with that of the earlier ones. Does this contrast point to behavioral changes in the Neandertal population?
We don't yet know what selective balance acted on the mobility pattern of Neandertals. Further, we don't know to what extent environmental changes (such as mobility patterns induced by cultural changes) may have affected the expression of the relevant anatomies. It is often assumed that these two mechanisms of change -- selective and environmental -- are concordant in direction, and so may be explicable in terms of the same ultimate causes. Thus, a change in mobility might both initiate direct environmental changes due to a changing pattern of muscle action on the bone; at the same time, the bone may be under selection to better match the pattern of muscle forces upon it. But there is really no justification for such an assumption; one might as easily argue that a decrease in muscle force induced by nongenetic causes results in a random change in selection on the cross-sectional anatomy. It does seem likely that developmental plasticity is the first explanation for changes; which puts the muscle forces themselves to the fore.
For most Neandertals, the femur is relatively short, has relatively large proximal and distal articular surfaces, has an anteroposteriorly curved shaft, and has a shaft cross section that is broader mediolaterally than anteroposteriorly, without a pronounced pilaster. I would suggest two hypotheses to explain the Neandertal bone geometry:
- Neandertal mobility was highly constrained by their short legs, which were themselves primarily adapted to climate. The restriction in mobility was mediated by a higher energetic cost of locomotion, which favored a residence pattern with less annual and daily movement.
- The requirements of hunting or other activities (including the possibility of conflict) in Neandertals demanded powerful limbs, loaded in many different directions, and did not accentuate long-distance daily or annual movements.
Although these explanations are not mutually exclusive, I tend to think the second hypothesis is the more likely one. With their relatively extreme body proportions, Neandertals were certainly at an energetic disadvantage in locomotion, but much of that energetic expenditure would have been inevitably lost to heat production, whether the Neandertals were moving around or not. Just living in a cold place exerts a high energetic cost, and the adaptive value of short legs is not merely in reducing surface area but also in increasing heat production. So the very high energy budgets of Neandertals give little reason to think that energy constraints were a decisive influence on their activity patterns.
The late Neandertals Les-Rochers-de-Villeneuve and Saint-Césaire appear to have retained the short femora and curvature, but have a cross-sectional geometry at midshaft that is more circular, with a relatively greater anteroposterior diameter. If the first hypothesis were true, then we have two options to explain the change:
- Climate change or competition with modern humans forced late Neandertals to become more mobile than their ancestors. This change in activity pattern would have imposed a high energetic cost because of their short legs.
- Cultural change enabled a more efficient foraging pattern (e.g. one based on Chatelperronian technology). This change allowed greater mobility because it relaxed the energetic constraints on Neandertal groups.
If in contrast, the second hypothesis were true (as I think likely) then the change apparent in later Neandertals would be explained by a change in foraging (specifically hunting) style. We may relate this change to the archaeological changes evidenced for the latest Neandertals, and indeed these technical changes may also have had energetic consequences, particularly if the technologies of the initial Upper Paleolithic helped to reduce the impact of cold, or if they enabled more energetically efficient foraging or hunting.
All this must be considered extremely tenuous, since it is not really testable with the information at hand. For the latest Neandertals, this is more or less always the case: the number of specimens is pretty small, and for most comparisons the sample size is therefore insufficient to show significant differences. But there are exceptions to this (supraorbital torus size and projection are two, presence of a chin is another), and with the right method, we might find that the postcranial evidence for change in this later sample is stronger than one might think.
References:
Beauval C. et al. 2005. A late Neandertal femur from Les Rochers-de-Villeneuve, France. Proc Nat Acad Sci USA PNAS Online
Holt BM. 2003. Mobility in Upper Paleolithic and Mesolithic Europe: Evidence from the lower limb. Am J Phys Anthropol 122:200-215. Wiley InterScience
Lieberman D. 2000. Comment on Pearson, OM, "Activity, climate, and postcranial robusticity." Curr Anthropol 594-595.
Pearson OM. 2000. Activity, climate, and postcranial robusticity. Curr Anthropol 41:569-607. Current Anthropology
Stock J and Pfeiffer S. 2001. Linking structural variability in long-bone diaphyses to habitual behaviors: foragers from the southern African Later Stone Age and the Andaman Islands. Am J Phys Anthropol 115:337-348.
Trinkaus E, Ruff CB, Churchill SE, Vandermeersch B. 1998. Locomotion and body proportions of the Saint-Césaire 1 Chatelperronian Neandertal. Proc Nat Acad Sci USA 95:5836-5840.
Weaver TD. 2003. The shape of the Neandertal femur is primarily the consequence of a hyperpolar body form. Proc Nat Acad Sci USA 100:6926-6929.
Neandertal tooth development and somatic development
Roberto Macchiarelli and colleagues (2006, link) have published data regarding molar crown formation times in Neandertals. Here is their abstract:
Growth and development are both fundamental components of demographic structure and life history strategy. Together with information about developmental timing they ultimately contribute to a better understanding of Neanderthal extinction. Primate molar tooth development tracks the pace of life history evolution most closely, and tooth histology reveals a record of birth as well as the timing of crown and root growth. High-resolution micro-computed tomography now allows us to image complex structures and uncover subtle differences in adult tooth morphology that are determined early in embryonic development. Here we show that the timing of molar crown and root completion in Neanderthals matches those known for modern humans but that a more complex enamel-dentine junction morphology and a late peak in root extension rate sets them apart. Previous predictions about Neanderthal growth, based only on anterior tooth surfaces, were necessarily speculative. These data are the first on internal molar microstructure; they firmly place key Neanderthal life history variables within those known for modern humans.
The ScienceNOW article by Ann Gibbons stresses the fact that the study involves sectioned teeth instead of external perikymata counts. The result is a lack of any significant difference between the timing and duration of crown formation compared to modern humans:
When the researchers sliced thin sections of the molars, they noticed important similarities between Neandertals and modern humans. The dark birth line emerged at about the same time in dental development as in modern humans, indicating that Neandertal teeth developed at the same rate as modern human teeth do around the time of birth, the team reports online today in Nature. The researchers also found that the crowns and roots of the Neandertals grew at the same rate of those of modern humans, with root growth complete by age 9 as in modern children. "This all points to a dental developmental schedule that was most like that in modern humans," says anatomist and lead author Christopher Dean of University College London, who also is a dentist.
The tooth development story is becoming a bit complicated to follow. As applied to Neandertals, Guatelli-Steinberg and colleagues (2005), and Ramirez Rossi and Bermudez de Castro (2004) assessed dental maturation rates from anterior teeth (incisors and canines), while the current paper by Macchiarelli and colleagues (2006) is about molar development. Additionally Dean and colleagues (2001) examined early Homo and Australopithecus samples, and Ramirez Rossi and Bermudez de Castro also considered earlier Spanish Homo samples.
The notable finding by Guatelli-Steinberg and colleagues (2005) was that modern human samples are themselves hugely variable in their enamel formation times -- at least, as interpreted through enamel tissue characters. This is a very serious problem for interpreting any past population characteristics, because in fact the variation among modern sample means -- without even considering the within-sample variation -- encompasses most fossil samples of Homo and many australopithecines as well.
Here's what I wrote about this last year:
[T]he Neandertals are far from the most interesting part of this perikymata problem. Can we tell a human from an australopithecine from these data? If so, why do some of the earliest humans have the lowest (i.e. sub-australopithecine) counts?
The early human specimen that stood out (considering their anterior dentition) was KNM-ER 15000, and it is not clear from the available papers whether it is actually outside the extant modern sample ranges. Otherwise, early Homo specimens are entirely humanlike in their crown formation times, and this observation is confirmed by Macchiarelli and colleagues' present work on Neandertal molars.
In short, early Homo enamel formation times (and for that matter, non-robust australopithecines) fall entirely within the range of variation of living humans, with most specimens within the range of human population means.
The null hypothesis in this case is that enamel formation times did not differ between fossil and living humans. That hypothesis is not refuted by the available data -- and given the wide variation in enamel formation times among living human populations, it seems likely that further sampling of fossil Homo will arrive at the same result. The issue is not sample size for the fossils, in other words, it is the intrinsic variability among living people, which remains unexplained.
The variation among living humans raises a thornier problem, also. The reason why many people are interested in molar enamel deposition is the idea that enamel formation is linked to somatic maturation in general. But the great variability in enamel formation times in recent humans would seem to disprove a strong link between somatic and dental maturation.
The idea that somatic and dental maturation rates should be tightly linked comes mainly from interspecific comparisons. For example, Ramirez Rossi and Bermudez de Castro (2004:938) draw out the following logic:
Dental growth is a good proxy for the overall rate of maturation in a species (Smith 1989). Short crown formation time in fossil Homo species therefore indicates that somatic development was not as long as in H. sapiens. Importantly, Neanderthals apparently also had a faster pace of somatic development than their ancestor, H. heidelbergensis.
...
A prolonged life-history in hominids has previously been related to a reduction in the mortality rate of adults, and in turn low mortality rates have in the past been associated with an increase in brain size. Metabolic rate has also been linked to brain growth and has been implicated as a primary determinant of variation in life history. However, developmental changes are most probably related to fundamental changes in the timing and frequency of reproduction. Results presented here suggest that brain growth and brain size are not primary determinants of life-history re-scheduling in hominids; rather, it seems that high adult mortality rates are most likely to have driven such rescheduling among Neanderthals. A clearer picture of Neanderthals emerges here--as a species of Homo adapted to particular environmental conditions, when a high-calorie diet and a high metabolic rate were able to fuel fast somatic growth, as well as to grow and sustain a large brain.
This last conclusion was rejected by Guatelli-Steinberg et al. (2005) -- after all, their data showed that Neandertals didn't have short enamel development compared to living Africans.
And reflecting on the balance of data from Neandertals, an especially rapid rate of development seems quite implausible. For instance, if Neandertals had no problem fueling a 3000-5000 kcal per day energy expenditure, then why did their kids have so many enamel hypoplasias? If Neandertals had a limitless tap of food to enable their rapid somatic development, then what killed them so young?
Guatelli-Steinberg et al. (2005) posit that dental development does not provide an adequate correlate of somatic maturation, and suggest that adult brain size makes a better yardstick:
It has also been suggested that if Neandertals suffered high adult mortality rates, then they might be expected to have had abbreviated periods of childhood growth (10, 15). Adult mortality rates directly select for the timing of maturation across mammals; a larger risk of dying selects for rapid maturation (9, 30, 31). However, Smith (32) notes that if Neandertals had accelerated life histories, then this would leave them with a "peculiar" relationship between brain size and maturation, "two variables that are rarely of step [sic]." Because large brains require extended periods of childhood growth (1-7, 33), the presence of large brains in Neandertals suggests that their adult mortality risks were not high enough to have prevented them from evolving prolonged growth periods.
The logic is that a given adult brain volume is linked to maturation schedule because of learning. Crudely, a larger brain takes longer to fill with information. Or more properly (in causal terms), selection for more information processing tends to increase brain size (relative to body size), information processing ability is constrained by learning, so that brain size is correlated to maturation schedule by indirect causal mechanisms.
But I would question even this relationship. For one thing, it doesn't seem to work very well within a population. Or at least, not within the population of living humans, where variation in brain sizes show no clear relationship to skeletal maturation schedules. For another, brain sizes have shrunk in recent humans, but there is no particular evidence that maturation times have reduced, or that humans have less to learn. Some of the smaller brain sizes may be explained by smaller body size, but smaller body size also ought to be correlated with faster maturation.
It seems to me that comparing Neandertals to living people for developmental rates is misleading. Living people are different from other primates in their very low rates of adult mortality (and consequent long period of post-reproductive senescence). And we know that Neandertals were more similar to other primates in this respect: they died younger than humans. But that isn't a new development in Neandertals -- instead, the long lifespans typical of recent people are the new development.
There has as yet been little integration of the literature on human growth with these fossil-related questions. For instance, many nutritionally-limited human populations respond by delaying growth. Sometimes such delays can be resolved by rapid growth later in development, sometimes they lead to reductions in adult body size. This kind of plasticity in growth schedules and ultimate body size ought to have characterized ancient humans, which would have increased their variability (in both maturation schedule and adult body size) compared to any single living human population.
References:
Guatelli-Steinberg D, Reid DJ, Bishop TA, Larsen CS. 2005. Anterior tooth growth periods in Neandertals were comparable to those of modern humans. Proc Nat Acad Sci USA 102:14197-14202. Abstract
Dean C, Leakey MG, Reid D, Schrenk F, Schwartz GT, Stringer C, Walker A. 2001. Growth processes in teeth distinguish modern humans from Homo erectus and earlier hominins. Nature 414:628-631.
Macchiarelli R, Bondioli L, Debénath A, Mazurier A, Tournepiche J-F, Birch W, Dean C. 2006. How Neanderthal teeth grew. Nature (early online) DOI link
Ramirez Rossi FV, Bermudez de Castro JM. 2004. Surprisingly rapid growth in Neanderthals. Nature 428:936-939. Full text (subscription)
Mellars on Neandertal-modern coexistence
Reuters is reporting on a study by Paul Mellars [UPDATE (8/31/05): Brad Gravina] and others concerning Neandertal-modern archaeological coexistence. Apparently, they have documented the interleaving of an Aurignacian level between two levels "attributed to Neanderthals".
The report says that the study is in this week's Nature. It isn't. So, I'll post again when I can find the paper.
It's not exactly clear to me what is new here. This is what Richard Klein wrote in 2003 (summary) about the archaeological interleaving of "Neandertal" and "modern" archaeological remains:
Evidence for cultural contact is also sparse, except for one well-documented case from central France. Here, a site occupied by Neanderthals shortly before their disappearance has provided an undeniable mix of Middle and Upper Paleolithic artifact types, including well-made bone tools and jewelry. It also contains the only indisputable house ruin from a Neanderthal site.
The current work refers to a different site, but the results are certainly not a surprise. Another case of Neandertal non-news news.
And Reuters adds insult to injury by posting the story with a picture of a Chinese woman looking at a reconstruction of Peking Man!
Now, if they actually found a modern human fossil in association with their "modern human" "Aurignacian" tools, that would be news!
UPDATE: A reader has kindly sent me the complete paper, discussed in a later post. Apologies to study author Brad Gravina, since my initial post followed Reuters in giving primary credit for the Chatelperron research to Paul Mellars; Mellars is a coauthor of the study.
References:
Klein RG. 2003. Whither the Neanderthals? Science 299:1525-1527. Summary
The Neandertal mtDNA story::2004 edition
Both of these papers add to our knowledge about the genetic variation of Neandertals and their genetic relationships--at least for their mitochondrial DNA--with succeeding populations of modern humans. Both of them also are freely available from the Public Library of Science, with links below.
Serre and colleagues expanded on the sample of four mtDNA sequences by attempting to find DNA traces in the 24 Neandertals fossils and 40 early modern human remains. The previous sample included two fossils from Feldhofer cave, one fossil from Vindija cave, and one from Mezmaiskaya cave in the Caucasus. For these four samples, the results have been relatively clear: the 4 Neandertals have mtDNA that is very closely similar, and as a group they differ from all known modern human sequences.
The new research used the knowledge that known non-Neandertal sequences are very divergent from modern humans as a way to identify Neandertal-like sequences by probing directly for them. This allowed a relatively rapid characterization of whether fossils preserved evidence of Neandertal affinities, without labor-intensive cloning or sequencing of ancient DNA. Out of the samples that they examined, 4 Neandertal remains and five early modern humans were preserved sufficiently to suggest that DNA might have survived. The 4 Neandertals included in two specimens from Vindija, Vi-77and Vi-80, Engis 2, and La-Chapelle-aux-Saints. All four of the specimens appeared to preserve sequences similar to the known sample of Neandertal sequences. In contrast the five modern humans, including Mladec 25c, Mladec 2, Cro-Magnon, Abri Pataud, and La Madeleine, did not amplify using the Neandertal primer despite the appearance of DNA preservation. Sarah and colleagues took their results as evidence that Neandertal-like DNA sequences disappeared along with the Neandertals, and were not preserved in any known modern human remains.
There are some weaknesses in the study design, which the authors acknowledge. Although they surveyed modern human remains for Neandertal-like sequences, they were unable to look for modern-like sequences in Neandertal remains. There is indirect evidence to suggest that they wouldn't have found such sequences anyway, since the four Neandertals and that appeared to present evidence of DNA preservation all amplified with the Neandertal primer. But those who have questioned Neandertal results because they could not distinguish modern-like sequences from contamination have not had their questions answered here. The fact that none of the modern human remains preserved Neandertal-like sequences is the important result. This adds to evidence from one prior study (Caramelli et al. 2003), which sequenced two individuals from Paglicci cave dating to around 24,000 years ago in southern Italy. Like the modern remains in this study, the Paglicci remains showed no evidence of Neandertal contribution.
The second study, by Currat and Excoffier, attempts to model of the movement of modern humans into Europe as they replaced the Neandertals. The motivation for this study was the unrealistic nature of earlier attempts to model this movement and its effects on DNA variation. In essence, earlier analysts like Nordborg (1998) assumed an island model in which the Neandertals and modern humans comprised two gene pools from which later European DNA might or might not have been drawn. Given this type of simple model, it is possible to work out the minimum ratio of Neandertal to modern human contribution that would be possible given the observed absence of Neandertal mtDNA sequences in the succeeding population of Europeans. In other words, these attempts were ways to determine the prior probability of certain mixtures of ancient populations on the basis of the observed frequency of their alleles in recent humans: of course, under the special case where the observed frequency of one of their alleles is zero.
Two pieces of evidence have tended to improve our ability to make these kinds of estimates. One of them is the increasing availability of samples immediately succeeding the disappearance of the Neandertals. Presumably, if Neandertals mitochondrial DNA survived it would have a higher frequency in these early populations than it does in living Europeans. At present, the frequency of Neandertal-like sequences in living Europeans is zero, and the number of early modern Europeans with Neandertal-like sequences also may be zero, although it is possible that at least one specimen does present such a combination (Hawks and Wolpoff 2001).
The second source of evidence concerns the possible demography of ancient humans. It is in this realm that the paper by Currat and Escoffier makes its contribution. The study incorporates two assumptions that attempt to model the complex interaction of Neandertal and early modern populations. The first assumption is that the two populations did not mix instantaneously with each other, but instead coexisted alongside each other for a long period or time. The second assumptions is that the two populations did not mix throughout their entire range over this time period, but instead mainly interacted along a wave front of dispersing modern humans. The effective both of these assumptions is to increase the expected importance of Neandertal genes in the modern human gene pool. The assumption of a long coexistence gives Neandertals added opportunities to mate with modern humans, while the assumption of a spreading wave of moderns adds the potential that some areas of Europe would have relatively high Neandertal contributions even if the overall level of Neandertal genetic contribution was low. The authors actually ran several different demographic scenarios to find a range of results.
They found that all of their models are united in expecting a greater contribution of Neandertal mtDNA than the simple instantaneous mixture model. In the slightly-backward logic of the problem, the data (which indicate no evidence of Neandertal mtDNA in living Europeans) make at least one of the following conditions unlikely: that Neandertals had a substantial level of mtDNA exchange with modern human populations, or that Neandertals survived alongside modern humans for a substantial length of time. In other words, under the assumptions of the models used here, Neandertals are very unlikely to have mixed with modern humans spreading into Europe to replace them.
Of course, the problem with any of these studies is in the assumptions that they require. For my part, I think the demographic assumptions of Currat and Excoffier are relatively unobjectionable, and certainly an improvement over those used by Serre and colleagues and earlier studies. But neither of the studies cites the really important paper in this regard, that of Mandersheid and Rogers (1996). In that paper, for the first time, the authors worked out the genetic consequences of demographic assertions about the Neandertal-modern transition. They found that Neandertal genes were quite unlikely to have gone extinct in an expanding post-Neandertal population, unless the Neandertals themselves had failed to contribute to that population. After this paper, the consequences of the Neandertal problem under purely neutral assumptions (like those used by Nordborg 1998) were really irrelevant anyway. Currat and Excoffier add a dimension of complexity to the problem, and therefore a further note of realism, but their conclusion was foregone.
The real elephant under the rug of these papers (or as I've said elsewhere, the 800-pound gorilla) is natural selection. Both of the papers rely on the assumption that mtDNA is neutral. This is, in a sense, necessary to the papers' existence, since without this assumption mtDNA may be considered to be completely uninformative about the Neandertal problem. But there are good reasons to think that mtDNA has been under positive selection recently in human prehistory. Most notable among these reasons is the fact that human mtDNA violates every test of neutrality. Also suggestive is the limited mtDNA variation among the known Neandertal sequences--a suggestion that the positive selection that has affected human mtDNA recently may be just the most recent of several episodes throughout human evolution. Until papers like these take the issue of selection seriously, there is little chance of finding consensus on the Neandertal genetic problem.
I have written about the interpretation of Neandertal mtDNA elsewhere as well.
References
@article{Caramelli:2003,
author = {David Caramelli and Carles Lalueza-Fox and Cristiano Vernesi
and Martina Lari and Antonella Casoli and Francesco Mallegni and
Brunetto Chiarelli and Isabelle Dpanloup and Jaume Bertranpetit
and Guido Barbujani and Giorgio Bertorelle},
year = {2003},
title = {Evidence for a genetic discontinuity between Neandertals
and 24,000-year-old anatomically modern Europeans},
journal = pnas,
volume = {100},
number = {11},
pages = {6593--6597} }
@article{Currat:2004,
author = {Mathias Currat and Laurent Excoffier},
year = {2004},
title = {Modern humans did not admix with Neanderthals during their
range expansion into Europe},
journal = plosbiol,
volume = {2},
number = {12},
pages = {e421} }
@article{Serre:2004,
author = {David Serre and Andr\'e Langaney and Mario Chech and
Maria Teschler-Nicola and Maja Paunovic and Philippe Mennecier
and Michael Hofreiter and G\"oran Possnert and Svante P\"a\"abo},
year = {2004},
title = {No evidence of {Neandertal} {mtDNA} contribution to early
modern humans},
journal = plosbiol,
volume = {2},
number = {3},
pages = {0313--0317} }
Neandertal teeth: the other shoe
The paper by Guatelli-Steinberg et al. (2005), earlier referred to here, is now available online from PNAS.
The results are basically as reported by National Geographic, finding that Neandertal anterior teeth have perikymata counts within the range of living human populations. Perikymata are microscopic ridges on the enamel surface of teeth; they mark the incremental growth of the teeth over small periods of time. The idea has been that these ridges work a bit like tree rings; they mark the amount of time that the tooth took to grow. However, as this study indicates, the formation of perikymata is not quite so simple as the addition of tree rings, and human populations actually vary substantially in the number of perikymata on their teeth.
What makes this different from earlier work (like Ramirez Rossi and Bermudez de Castro 2004) is the inclusion of an African sample. The very low perikymata count of the recent Africans significantly extends the range, which had previously been assessed in Europeans only. Thus, the conclusion here is that there is no evidence from perikymata to indicate that Neandertal development was any different from that within living human populations.
Now we can wait for the other shoe to drop:
The finding from the African population sampled here shows that some developmentally normal humans have much lower perikymata counts than others. This varies by tooth (since they don't all develop for the same time): the lower canines have the highest counts, with a mean over 150; the lower incisors have the lowest counts with a mean down near 100. Remember that these values are means; individuals in the sample must have scored lower, although the range of the sample is not reported in the paper.
With this sample, the human range encompasses the Neandertals. It encompasses all the earlier European hominids (chiefly from Atapuerca) sampled by Ramirez Rossi and Bermudez de Castro (2004), because these hominids had counts higher than Neandertals.
Let's take a look at Dean et al. (2001:628), who give values for earlier hominids. Here's a table including some earlier hominids along with the South African values from Guatelli-Steinberg et al. (2005). The current paper does not include the numbers, so I am reading estimates off the figure, but considering they are means and the important aspect is the total range, the numbers aren't critical. Lower numbers are less like the recent Europeans that were the standard before the new comparative work.
| Sample | UI1 | UI2 | UC | LI1 | LI2 | LC |
| Recent South African | 120 | 117 | 135 | 105 | 110 | 155 |
| Sangiran 4 | 138 | |||||
| SK 27 | 153 | |||||
| KNM-ER 1590 | 114 | 127 | ||||
| KNM-ER 820 | 113 | |||||
| KNM-WT 15000 | 94 | 96 | 100 | 96 | 92 | 110 |
| Paranthropus | 83 | 85 | 112 | 78 | 90 | 103 |
| Australopithecus | 123 | 109 | 122 | 116 | 122 | 143 |
From these numbers, Sangiran 4 and SK 27 are within the range of modern human population means. So are three of the teeth of Australopithecus (i.e. A. africanus), and the remaining three teeth are pretty close, so that it seems likely the A. africanus dentition wasn't very different in its perikymata number from the range of living Africans.
The standouts are KNM-WT 15000 and Paranthropus (i.e. A. robustus). A. robustus is easy to explain: its anterior teeth are a lot smaller than ours. A lot smaller. If enamel formation rates were similar, then they ought to have taken less time to form, regardless of other aspects of somatic development.
The puzzle is KNM-WT 15000, the famous Nariokotome skeleton. Is this skeleton a normal representative of early human populations? Is it at the extremely low end of a normal range including others like KNM-ER 1590 (also a bit smaller than the mean, although probably not outside the range of living Africans)? Is it pathological?
The other shoe is the research paper that will cover all these questions.
Now it could be that these numbers really aren't comparable for some reason; I don't do perikymata, but I can tell that the counts depend on estimates of crown height and packing density, so it's not obvious that they were derived in the same way (although the papers do share one author).
But the Neandertals are far from the most interesting part of this perikymata problem. Can we tell a human from an australopithecine from these data? If so, why do some of the earliest humans have the lowest (i.e. sub-australopithecine) counts?
I think we can disregard the idea that their somatic development rates were "highly derived" in a non-human-like direction. It's not like they're Neandertals, after all.
References:
Guatelli-Steinberg D, Reid DJ, Bishop TA, Larsen CS. 2005. Anterior tooth growth periods in Neandertals were comparable to those of modern humans. Proc Nat Acad Sci USA 102:14197-14202. Abstract
Dean C, Leakey MG, Reid D, Schrenk F, Schwartz GT, Stringer C, Walker A. 2001. Growth processes in teeth distinguish modern humans from Homo erectus and earlier hominins. Nature 414:628-631.
Ramirez Rossi FV, Bermudez de Castro JM. 2004. Surprisingly rapid growth in Neanderthals. Nature 428:936-939. Full text (subscription)
Metrosexual Neandertals
Paleoanthropology defines the "slow news cycle". What else can explain The Independent (UK) picking up this six-month-old story about Gary Sawyer's and Blaine Maley's Neandertal "reconstruction" (via Anne Gilbert at Palanthsci)? Perhaps it's the compelling power of the AMNH press release?
I'm drawing attention to it because it contains the first public expression I can remember of the "sensitive Neandertal" theory:
Whereas Homo sapiens was able to pursue prey over very long distances, Neanderthals appear to have been markedly less able to do so and would probably therefore have had to have been more confrontational with their potential dinners.
As a consequence, Neanderthal males were probably away from their families for shorter periods than Homo sapiens - and it is likely that family structures and relationships between males and females may well have been markedly different.
"Markedly different" meaning more cohesive, stable and caring, evidently. The headline?
Official: Neanderthal Man was not a hairy oaf but a sensitive kinda guy
Carson would be so proud.
How does a paleoanthropologist react to this news?
"The reconstruction strengthens the case for regarding Neanderthals as representing a different species with their own survival strategies compared to those of Homo sapiens," said Professor Chris Stringer, head of the Human Origins Research Programme at London's Natural History Museum.
"The work shows how different strategies resulted from and reinforced different evolutionary paths," said Professor Stringer, author of a recent book on hominid prehistory, The Complete World of Human Evolution.
Hmmm. Either, (a) we are now ready to confirm that a caring man cannot be a member of the human species, or (b) no matter what feature somebody discovers, there will be somebody else to claim it puts Neandertals on a separate evolutionary path.
Maybe it's my Neandertal genes that make me act out when I see this kind of thing.
UPDATE (9/12/05): I have an e-mail from Chris Stringer letting me know that people are getting in touch with him about the post. Please leave the poor man alone -- he was clearly commenting generally on the reconstruction and not the headline! The humor in the story is the juxtaposition!
Body mass in ancient humans and high latitude populations
Chris Ruff and colleagues (2005) provide additional statistics on body mass in high latitude populations, including Inupiat and Finns. The importance of the paper is that previous regressions to estimate body mass in fossil humans have been based on lower-latitude populations. High latitude populations with broader pelves might be expected to have a slightly different mass than would be predicted for lower latitude populations, so adding the new samples ought to improve accuracy of estimation. Ruff and colleagues found that the new samples did result in slightly higher estimates of body mass for fossil Neandertals and other high latitude samples (including earlier and later Europeans and the Jinniushan skeleton from northern China). These estimates were not very far from the original estimates based on the earlier comparative sample, though, so the effect is minor.
Whenever I see estimates like these, they serve as a reality check of sorts about the common knowledge that Neandertals were massive and stocky in body form. The new body mass estimates for Neandertals are 75.8 kg (166 lb) for La Chapelle-aux-Saints and 82.3 kg (181 lb) for Kebara. When I was in high school, I was pretty lean myself and I wrestled in the 185 pound weight class. In other words, these massive Neandertals were nothing like the people we consider to be massive today.
On the other hand, they were hunter-gatherers, so we are in a whole different world in terms of fatness. Ethnographic hunter-gatherers are relatively small in terms of both mass and stature. But then, ethnographic hunter-gatherers tend to live in relatively marginal environments with more or less severe scarcity of resources. To give a bit of scale, Katzmarzyk and Leonard (1998) report on body mass in populations with different mean temperature. The sample is not huge, but it is illustrative:
Body mass against climate, from Katzmarzyk and Leonard 1998.
The red line on the chart I inserted at the body mass of La Chapelle. It is slightly large for an Eskimo, and slightly larger for an African (although notably not for a Polynesian). The important point is that the Neandertals were really not all that large compared to today's humans, whether we look at industrialized societies or not. If we accept the large size of a few specimens as indications of a large average mass in the population, this population is still not striking. Ruff (2002) provides a good review of the variation in body size in recent and living human populations. Considering the evidence that human body size has decreased over the terminal Pleistocene and Holocene, Neandertals would appear to be even closer to us and to contemporary populations.
Neandertals mainly appear to stand apart because of the contrast between them and later Europeans. This contrast mainly stems from the taller stature of later people, but in addition to an increase in height there was also a reduction in pelvic breadth. Overall, this appears to indicate a smaller mass for Upper Paleolithic Europeans, although the sample of individuals with both stature and bi-iliac measurements is very small (n = 6 in Ruff et al. 2005).
Ruff (2002:217) presents the following hypothesis:
One possible explanation for these observations is that the Late Pleistocene reduction in body size was due primarily to genetic factors, possibly reduced selection for large body size in association with technological improvements (Frayer 1984), whereas the succeeding fluctuations (decrease, then, in higher latitudes, increase) in body size in the Holocene were due to environmental effects on growth, e.g., nutrition.
The first part of this hypothesis begs for testing. An alternative is that the dietary changes that led to nutritional deficits in growing people were established long before the Holocene when agricultural subsistence patterns appeared. With their constant technological improvements, Upper Paleolithic people appear to be working much harder for their subsistence than Neandertals. Or social stratification may have led to inequities in food access that likewise had developmental consequences. One might even imagine that delayed maturation was an adaptation to restriction in calories or micronutrients during development -- which might make sense considering that undernourished populations today exhibit slower developmental times and delayed maturation compared to Westernized populations.
Of course if there was no mass reduction in Upper Paleolithic people, the first part of the hypothesis is moot.
As a bottom line, Neandertals were pretty clearly distinctive in their body proportions, by having broad pelves, short distal limb segments, and relatively short statures. But this distinctiveness did not necessarily extend to greater body mass, especially in comparison to contemporary and earlier humans, and present-day Europeans. If you have an image of Neandertals as hulking, muscle-bound brutes (or hulking, muscle-bound hunks, depending on your taste), then please consider that in Olympic boxing terms, La Chapelle's mass of 75.8 kg is just above the border between middleweight and light heavyweight, two classes below the maximum. The real heavyweights (i.e. super heavyweight class) start at full 14 stone, or 91.6 kg. That includes the pelvis from Atapuerca, but so far no other fossil humans.
References:
Katzmarzyk PT and Leonard WR. 1998. Climatic influences on human body size and proportions: Ecological adaptations and secular trends. Am J Phys Anthropol 106:483-503. Wiley InterScience
Ruff C. 2002. Variation in human body size and shape. Ann Rev Anthropol 31:211-232. Annual Reviews
Ruff C, Niskanen M, Junno J-A, Jamison P. 2005. Body mass prediction from stature and bi-iliac breadth in two high latitude populations, with application to earlier higher latitude humans. J Hum Evol 48:381-392.
The (non-) autapomorphic ramus of Neandertals
Wolpoff and Frayer (2005) pick up the question of whether the Neandertal mandibular ramus presents features absent in other humans, recent or archaic. Here's the abstract:
The ramus of Neandertal mandibles is said to show a suite of uniquely Neandertal character states that demonstrate the independent course of Neandertal evolution. This is the latest of numerous attempts to define cranial and mandibular autapomorphies for Neandertals. We examine variation in the four presumably autapomorphic ramal features and show they are neither monomorhic within Neandertals (to the contrary Neandertals are at least as variable as other human samples) nor unique to Neandertals, since they regularly appear in populations predating and postdating them. Neandertals differ from other human populations, both contemporary and recent, but the question of whether this fact reflects a divergent evolutionary trajectory must be addressed by the pattern of differences. In this case, as in the other attempts to establish Neandertal autapomorphies, rather than showing restricted variation and increased specialization, the Neandertal sample shows that the range of human variation in the recent past encompasses, and in some cases exceeds, human variation today, even in the very features claimed to be autapomorphic.
The four features examined are the position of the lowest point in the mandibular notch (posterior or central), the height of the coronoid process relative to the condyle, the position where the crest of the mandibular notch meets the condyle (central or lateral), and the depth of the mandibular notch (shallow in many Neandertals). They conclude:
The question we have addressed is not whether Neandertal ramal features differ from other samples; all populations vary and have their unique aspects, whether in unusual anatomies or in differing frequencies of anatomical variants. The question is whether Neandertals differ in a way that could be used to support the notion that they are a distinct clade, evolving for whatever reason in their own unique direction. Are there, in the words of Weidenreich (1943) cited above, "peculiarities which could be claimed as 'specialization,' thereby proving the deviating course this form has taken in evolution"? We believe the answer is no. The "distinctive" mandibular ramus features discussed here are not Neandertal autapomorphies. They are neither limited in their range of expression within Neandertals (to the contrary, Neandertals are at least as variable as other human samples) nor are they unique to Neandertals, since they appear in populations predating and postdating them (7).
I think if I could wrap up every paper with a Weidenreich quote I would.
References:
Wolpoff MH and Frayer DW. 2005. Unique ramus anatomy for Neandertals? Am J Phys Anthropol Early View
Nitric oxide in the sinuses of Neandertals
OK, I was reviewing hypotheses about sinus anatomy for a student, and I ran across this one, which I must admit was news to me:
Nitric oxide (NO), a substance produced in the paranasal sinuses, is thought to defend against pathogens among other functions. High levels of NO increase mucuciliary activity. NO levels in both the nasal cavity and the maxillary sinus seem to depend on the size of the paranasal ostia [i.e., the openings of the sinuses into the nasal cavity]: As ostia [sic] size increases, NO levels decrease. It has been hypothesized that the purportedlarge sinuses of Neandertals are a consequence of their need for high NO production to support a vigorous way of life (Rae and Koppe 2004:216).
No, nitric oxide is not laughing gas -- that's nitrous oxide (N2O)! Although for excellent pictures of laughing Neandertals, I highly recommend Kennis and Kennis (whose website, sadly, seems to have disappeared).
Rae and Koppe (2004) draw their account from this meetings abstract by Sam Marquez and colleagues (2002):
The anatomy and function of the Neanderthal upper respiratory tract (URT) has been a topic of great interest, particularly as a possible window on their lifestyles. Neanderthal paranasal sinuses (pns) have been described as expansive although the precise reasons for this are not well understood. However, the pns are the prime site for production of nitric oxide (NO), a gas with neurotransmitter-like functions. In the URT, NO exerts functions on ciliary activity, gland stimulation, and acts as an aerocrine messenger between the upper and lower airways that selectively reverses hypoxic pulmonary vasoconstriction without causing systemic vasodilation. NO also functions in host defense (Fliegelman, Gannon, and Lawson, 1998) insuring sterility of the pns permitting mucus drainage through their ostia into the airflow pathway thus serving as a valuable adjunct in the air-conditioning process of humidification (Gannon et al., 1997).
This qualitative and quantitative study examined pns morphology via CT imaging in a multiregional sample of 125 human skulls and compared them to assessments of the nasal complex in archaic Homo sapiens. Modern groups exhibited population specific pns morphology with respect to ecogeographic localities. Notably, Neanderthal pns dimensions differed from European modern populations. This suggests that Neanderthal pns volumes may reflect a different clade trajectory, perhaps due to differing NO production rate and utilization. We hypothesize that the idiosyncratically large size of Neanderthal pns is related to greater production of NO. This sinonasal / aerocrine adaptation was selected to meet the critical cardiopulmonary system demands imposed by the vigorous lifestyle of Neanderthals (Marquez et al. 2002:107).
Hopefully that research will come out somewhere. The beauty of the sinus production of NO is that it is localized to the respiratory tract. NO metabolism is very important to different systems -- its role as a vasodilator makes it an important regulator of blood pressure, it has a role in the reproductive system, and a role as a neurotransmitter. So it is important for its effects to be localized rather than systemic.
For Neandertals, one could imagine different kinds of balances -- for example, since NO concentration decreases with ostium size, a larger Neandertal ostium might require greater NO productivity to maintain the same function. It doesn't seem too likely that greater productivity was an adaptation to activity level, at least not unless high-activity modern populations were shown to have large sinuses. The Neandertals otherwise are a bit of a contradiction, since in general sinus size seems to decrease with latitude -- apparently a structural side effect of having larger nasal cavities in colder climates. I guess ostium size becomes a pretty crucial parameter to examine, since if large maxillary sinuses were merely a side effect of large faces in Neandertals, the nasal and sinus systems would presumably have evolved to maintain a constant function.
Rae and Koppe (2004) have a good review of other adaptive hypotheses for sinuses. I guess it will take some convincing to get me to think they are specifically adaptive in humans, since their morphology and size is so variable.
References:
Kirihene RKDRA, Rees G, Wormald P-J. 2002. The influence of the size of the maxillary sinus ostium on the nasal and sinus nitric oxide levels. Am J Rhinol 16:261-264. IngentaConnect
Marquez S, Gannon P, Lawson W, Reidenberg J, Laitman J. 2002. Were Neanderthals full of "NO" gas? The relationship between paranasal sinus morphology and nitric oxide production. Am J Phys Anthropol 34(suppl):107.
Rae TC, Koppe T. 2004. Holes in the head: evolutionary interpretations of the paranasal sinuses in catarrhines. Evol Anthropol 13:211-223. DOI link
The real Neanderthin
I was talking to some folks about the isotope values for Neandertals, and was immensely surprised to find out that nitrogen-15 (15N) proportions can be driven higher by weight loss.
Here's an abstract of an article from last year by Fuller and colleagues:
While past experiments on animals, birds, fish, and insects have shown changes in stable isotope ratios due to nutritional stress, there has been little research on this topic in humans. To address this issue, a small pilot study was conducted. Hair samples from eight pregnant women who experienced nutritional stress associated with the nausea and vomiting of morning sickness (hyperemesis gravidarum) were measured for carbon (delta13C) and nitrogen (delta15N) stable isotope ratios. The delta13C results showed no change during morning sickness or pregnancy when compared with pre-pregnancy values. In contrast, the delta15N values generally increased during periods of weight loss and/or restricted weight gain associated with morning sickness. With weight gain and recovery from nutritional stress, the hair delta15N values displayed a decreasing trend over the course of gestation towards birth. This study illustrates how delta15N values are not only affected by diet, but also by the nitrogen balance of an individual. Potential applications of this research include the development of diagnostic techniques for tracking eating disorders, disease states, and nitrogen balance in archaeological, medical, and forensic cases.
Last year, I reviewed some papers that documented high 15N values in Neandertals, which concluded that the high values may have resulted from mammoth and rhinoceros consumption. In another post, I explored the reasons why fish (also a high 15N dietary source) have been neglected as an explanation for the high Neandertal 15N values.
Now, the papers on these topics (e.g. Bocherens et al. 2005) have compared Neandertal isotopic ratios to those of other fauna from the same time period, so trophic level and other relations ought to be visible within this sample. But other evidence suggests that Neandertals were under high nutritional stress compared to most living human populations, including the high incidence of enamel hypoplasias, which are developmental deficits of tooth formation (Molnar and Molnar 1985).
Comparisons suggest that Neandertal nutritional stress was not outside the range of living populations, with a similarity in the proportion of linear enamel hypoplasia in Neandertal and Inuit samples (Guatelli-Steinberg et al. 2004). In isotopic terms, this is a difficult comparison, since Inuit do eat lots of fish, marine mammals and other 15N-enriched foods.
Another element of complexity is that 15N composition responds to weaning time, because breast milk is enriched in 15N content also. This effect diminishes during childhood after weaning, by around age 7-9, so it shouldn't affect adult Neandertal specimens, but I point it out because nutritional stress may also affect the age of weaning or dietary independence, which might conceivably deplete 15N in lactating women. One might imagine lactation balancing some of the 15N surplus resulting from pregnancy or nutritional stress.
So it may be awhile before we will know what the full effect of nutritional stress may be on these isotope values.
References:
Bocherens H, Drucker DG, Billiou D, Patou-Mathis M, Vandermeersch B. 2005. Isotopic evidence for diet and subsistence pattern of the Saint-Césaire I Neanderthal: review and use of a multi-source mixing model. J Hum Evol 49:71-87.
Fuller BT, Fuller JL, Sage NE, Harris DA, O'Connell TC Hedges RE. 2005. Nitrogen balance and delta15N: why you're not what you eat during nutritional stress. Rapid Commun Mass Spectrom 19:2497-2506. PubMed
Guatelli-Steinberg D, Larsen CS, Hutchinson DL. 2004. Prevalence and the duration of linear enamel hypoplasia: a comparative study of Neandertals and Inuit foragers. J Hum Evol 47:65-84. PubMed
Molnar S, Molnar IM. 1985. The incidence of enamel hypoplasia among the Krapina Neandertals. Am Anthropol 87:536-549. JSTOR
Schurr MR. 1998. Using stable nitrogen-isotopes to study weaning behavior in past populations. World Archaeol 30:327-342.
Linear enamel hypoplasia and nutritional status
I just wanted to take down a note about this paper from last year, along with a couple of older studies of linear enamel hypoplasia:
Brief Communication: Linear enamel hypoplasia and the shift from irregular to regular provisioning in Cayo Santiago rhesus monkeys (Macaca mulatta)
Debbie Guatelli-Steinberg, Zeynep Benderlioglu
This study investigates changes in the prevalence of linear enamel hypoplasia (LEH) before and after the shift from irregular to regular provisioning in the Cayo Santiago rhesus monkey population. Prior to 1956, monkeys on this island colony did not receive consistent provisions, and were reported to be in poor health (Rawlins and Kessler [1986] The Cayo Santiago Macaques; Albany: State University of New York Press). A regular provisioning program, instituted in August 1956, resulted in the improved health of individuals and the growth of the population (Rawlins and Kessler [1986] The Cayo Santiago Macaques; Albany: State University of New York Press). LEH, a developmental defect of enamel, is a sensitive indicator of systemic physiological stress (Goodman and Rose [1990] Yrbk. Phys. Anthropol. 33:59-110). It was therefore hypothesized that the prevalence of LEH would be higher in monkeys who were irregularly provisioned than in monkeys who experienced regular provisioning. To test this hypothesis, teeth were examined for LEH in a sample of 181 female rhesus monkeys. The results support the hypothesis: the mean number of defects was statistically significantly higher in the preprovisioned group than it was in the postprovisioned one. When LEH prevalence was assessed using only defects occurring on antimeric pairs, the preprovisioned group again had a higher prevalence than the postprovisioned one, although the difference was not statistically significant, most likely because of the reduced sample size. The results of this study indicate that changes in LEH prevalence, at least in this population of rhesus monkeys, are associated with changes in nutritional status.
Other studies have shown a relationship between LEH prevalence and malnutrition among human populations. The unique aspects of this study are that it shows the same relationship in another primate species, and that it shows the response to a change in nutritional levels.
This response was shown in a human context by Alan Goodman and colleagues in 1991:
Nutritional supplementation and the development of linear enamel hypoplasias in children from Tezonteopan, Mexico
AH Goodman, C Martinez and A Chavez
The purpose of this study was to compare the effect of nutritional intake during tooth-crown formation on the subsequent development of linear enamel hypoplasias (LEHs) in Mexican nonsupplemented (control) adolescents (n = 42) and adolescents who had received daily nutritional supplements since birth (n = 42). The proportion of individuals with LEHs was nearly two-fold greater (74.4%; 95% CI 64.7-84.1%) in the control than in the supplemented group (39.5%; 95% CI 28.6-50.4%; chi 2 = 9.44; P = 0.001). Although the estimated peak age at formation, approximately 2-2.5 y, is similar in both groups, the proportion of early (before 1.5 y) and late (after 3.0 y) LEHs was greater in the control group. LEH was also more common in females and was associated with an increase in illness days and a decrease in growth velocity. Results of this study suggest that mild to moderate undernutrition during enamel formation is causally linked to the formation of LEHs.
The distribution shows that the two samples actually are very similar in the incidence of LEH at the modal age of between 1.5 and 2.5 years. Plausibly, this is not only attributable to disease, but also stress associated with weaning; some degree of LEH incidence may be more resistant to change by nutritional supplementation. Goodman et al. (1991:780) wrote:
The greatest relative difference in freuqency of LEH between supplemented and control groups occurs before 1.5 y and after 3.0 y, or before and after weaning and the time of greatest illness. It is as if all children are at great risk of LEH immediately after weaning, but the supplemented individuals are afforded greater protection before and after weaning. These data also support the hypothesis that common respiratory and gastrointestinal illnesses are an immediate cause of LEH, especially in individuals with compromised nutritional status.
Richard May, Alan Goodman and Richard Meindl conducted similar observations in Guatemala, reported in 1993:
Response of bone and enamel formation to nutritional supplementation and morbidity among malnourished Guatemalan children
Richard L. May, Alan H. Goodman, Richard S. Meindl
Enamel matrix secretion responded positively to increased supplementation. Children who received less than 34.25 kcal/day in supplement had more LEH than those who received more supplement. No differences in ossification status were found between supplementation groups. These data suggest that enamel formation may be more sensitive to changes in nutritional status than is bone mineralization. Disruptions of bone and enamel formation were both associated with frequent illness. Children who were ill more than 3.6% of the time had more LEH and fewer ossified hand-wrist centers than children who were less frequently ill. Conclusions regarding relative environmental sensitivity must take into account the specific aspects of dental and skeletal development examined.
This last part is an observation that different teeth seem to be more or less resistant to enamel formation disruptions.
References:
Guatelli-Steinberg D, Benderlioglu Z. 2006. Linear enamel hypoplasia and the shift from irregular to regular provisioning in Cayo Santiago rhesus monkeys (Macaca mulatta). Am J Phys Anthropol 131:416-419. doi:10.1002/ajpa.20434
Goodman AH, Martinez C, Chavez A. 1991. Nutritional supplementation and the development of linear enamel hypoplasias in children from Tezonteopan, Mexico. Am J Clin Nutr 53:773-781.
May RL, Goodman AH, Meindl RS. 1993. Response of bone and enamel formation to nutritional supplementation and morbidity among malnourished Guatemalan children. Am J Phys Anthropol 92:37-51. doi:10.1002/ajpa.1330920104
No spongiform Neandertals, please
Julien Riel-Salvatore reviews some reasons why kuru did not wipe out the Neandertals.
I don't have anything to add. The hypothesis comes from a paper in Medical Hypotheses by Simon Underdown; here's part of the abstract:
TSEs could have infected Neanderthal groups as a result of general cannibalistic activity and brain tissue consumption in particular. Further infection could then have taken place through continued cannibalistic activity or via shared used of infected stone tools. A modern human hunter-gatherer proxy has been developed and applied as a hypothetical model to the Neanderthals. This hypothesis suggests that the impact of TSEs on the Neanderthals could have been dramatic and have played a large part in contributing to the processes of Neanderthal extinction.
The short paper is admittedly speculative but quite clear. It does fail to cite the literature about selection on the prion gene, PRNP (I discussed it here in early 2006).
Riel-Salvatore points out all the reasons why it is probably wrong:
1. Neandertals were eating each other 100,000 years before they went away.
2. Neandertals didn't live as long as most humans who develop TSE symptoms.
3. Neandertals lived at much lower densities than the Kuru-spreading Fore people, and it's not credible for them to have spread a prion disease by cannibalism across this space (although, the urine-dispersed CWD seems to do spread pretty well through deer).
4. Non-Neandertals have a clear record of altering human skeletal remains also, including African Middle Pleistocene and early Upper Paleolithic Europeans.
I think these points are fatal to the hypothesis, unless we resort to a different mode of transmission; but in that case there is no reason to suppose that a prion disease would be involved rather than a viral or bacterial agent. I should also mention that despite early claims, there is not any reason now to think that the human prion gene was under long balancing selection.
References:
Underdown S. 2008. A potential role for Transmissible Spongiform Encephalopathies in Neanderthal extinction. Med Hypotheses (in press) doi:10.1016/j.mehy.2007.12.014
Barbaric yawping about Neandertal women
This morning, my irritation level about this Neandertal women hunting story finally reached its boiling point. I unleashed a Neandertal-style cry of anguish -- which if you've never heard one, sounds remarkably like a Wookie-style cry of anguish.
Am I a simple misogynist? Does the idea of deerstalking Neandertal women threaten my manhood? Maybe, although Gretchen assures me I'm not. Mostly, I'm irritated because a full-text search of the paper yields no mention of any possible test of their idea.
I hate being so critical of this idea. I really like Kuhn's and Stiner's other work. But over half of people think that all our raving about ancient humans is fantasy anyway, so I try to be as critical as I can. And this is a real doozy.
It's bad enough for something like this to hit the New York Times. But this one has even invaded Instapundit. Clearly something must be done!
So, I told my class I was incapable of giving a normal lecture, and would continue on the subject of sexual division of labor until they found a satisfactory means of testing Kuhn and Stiner's hypothesis.
Unfortunately, my students actually like seeing me rant and tear out my hair, so they had a positive disincentive to find the right answer. So, if you want a job done right...
Eemian elephant-hunting French Neandertals
There aren't many details about the site, but the Independent has the best story about it:
French and Belgian archaeologists have found proof that Neanderthals - mankind's closest relatives - were living in near-tropical conditions, hunting rhinoceros and elephant, close to what is now France's Channel coast 125,000 years ago.
...
Jean-Luc Locht, a Belgian expert in prehistory at the French government's archaeological service, was a researcher at Caours. "This is a very important site, a unique site," he said. "It proves that Neanderthals thrived in a warm north-west Europe and hunted animals like the rhinoceros and the aurochs, just as they previously, and later, hunted ice-age species like the mammoth and the reindeer.
Can't wait to hear more.
More on Neandertal women hunting
Some readers have asked whether the skeletons of Neandertal females don't provide a test of the idea that they were hunting. For instance, could we find evidence on Neandertal female arm bones for the kind of spear-thrusting behavior that we believed Neandertals used?
Or maybe we would expect that hunting would reduce the level of sexual dimorphism in Neandertals. If women were smaller than men, the logic goes, then they would be less capable of the highly strenuous and athletic Neandertal hunting style, which involved direct confrontations with large animals.
The evidence that we have is (a) Neandertal women have beaten-up skeletons also, not significantly different from the men, although the number of injured Neandertal female skeletons is itself very, very small (b) there are not enough Neandertal women to really answer the question about limb bone use, and (c) they were not very different in their dimorphism than modern people.
The problem is that these data don't really answer the question. For instance, a hunting Neandertal woman might be expected to take a less risky role than the men, and that might be a role that didn't involve spear thrusting, or at least not nearly so much. So the limb bone use doesn't clearly test the hunting hypothesis.
Nor do injuries -- since Neandertal women could have been injured in many other ways besides hunting. In fact, if we really thought that Neandertal women should have taken a less risky role in hunting, then they should have fewer injuries attributable to hunting than men. Which makes it really problematic that they don't differ. The sample size of injuries is small enough that I don't think any special explanation is required.
And dimorphism probably can't predict foraging effort. For instance, female lions do most of the hunting within prides, but lions have high sexual dimorphism compared to humans. Large body size in males means that fitness increases with size, but it doesn't mean that foraging success increases with size.
To my mind, the key question is why females in carnivorous human societies don't hunt, when female carnivores do. The answer comes from life history. Human females have single births spaced several years apart, female carnivores (even large carnivores like lions) have litters spaced 1-2 years apart. Female humans cannot afford the kind of mortality risk faced by female lions, because of the much lower fecundity of humans.
That doesn't by itself preclude female hunting by early hominids, but it suggests that such hunting must have been constrained to situations where mortality risk was minimal (such as, several times lower than the mortality risk for hunting lions).
My own argument (made last week) is that Neandertal female foraging behavior was apparently flexible and plastic, so that female organizational strategies and sexual division of labor are unlikely to explain Neandertal extinction. Considering their flexibility, it would be unlikely that they never hunted, but such hunting could not have long persisted unless it was very low risk.